Exploration of novel dual heterocyclic‐fused vanillin derivatives as potential antifungal agents for crop disease control

Plant natural products, which serve as innate chemical defenses against pathogens and other invasive pests, are valuable resources for novel agrochemical innovation. Vanillin, a natural antimicrobial compound, has garnered significant attention in food and agrochemical industries in recent years. Forty-one heterocycle-fused vanillin derivatives were constructed by employing a structural splicing strategy. Bioassays demonstrated that compound 6 exhibited outstanding inhibitory activity against the spore germination of Fusarium oxysporum, with an IC50 value of 7.0 μg/mL. Compounds 3a, 6, 7f, and 8 f showed superior inhibitory activity against Botrytis cinerea spores, significantly outperforming their precursor vanillin and the positive controls, difenoconazole and hymexazol. Ten selected compounds inhibited the mycelial growth of Valsa mali, with IC50 values varying from 3.1 to 30.5 ug/mL. Compound 7'j with an IC50 value of 4.7 μg/mL showed superior inhibitory potency against the mycelial growth of Alternaria solani than commercial fungicides, hymexazol and carbendazim. In vivo bioassays confirmed the notable protective efficacy of compound 3a against B. cinerea and the marked therapeutic effect of compound 7'j against A. solani. Structure-activity relationship (SAR) analysis indicated that the combination of 1,3,4-oxadiazole and benzimidazole may be the optimal scaffolds for fungicidal activity. Cytotoxicity assays revealed low to moderate effects on human keratinocyte (HaCaT), suggesting acceptable mammalian safety profile under dermal exposure for these compounds. These findings demonstrate that the potent vanillin-derived analogs reported herein represent promising candidates for novel fungicide development.